In production plants which already have a high degree of automation, e.g. mills as well as feedstuff mills, a conflict of goals has recently developed in that an inexpensive increase in quantity is impossible with existing technical measuring means or is possible only at the cost of qualitative parameters. Increasingly higher installed throughput capacities with persistently strict demands on quality, particularly on the consistency of the quality, require a more precise controlling and monitoring of the production flows. Both the processing quantity and the instantaneous throughput must be constantly determined with weighing precision.
However, accurate weighing involves repeated filling of the weigher, measurement and emptying of the weigher, insofar as accurate weighing is understood to mean weighing by means of weighers which are calibrated by government technicians, and results in an intermittent transporting of the product. In order to overcome this disadvantage, intermediate compensating bins must be used in addition, but this necessitates additional costs. At present, belt weighers are used almost exclusively for continuously determining a production flow with respect to quantity with materials having unfavorable flowing properties, e.g. flour, flour mixtures, break, bran, etc., and for a continuous transporting of the product. Belt weighers have the great advantage that the problems of flow behavior of the product to be weighed have virtually no influence. The product is continuously guided on the weighing belt, weighed and discharged, likewise in a continuous manner. But this solution is disadvantageous in two respects. A belt weigher is less accurate than a classic hopper scale. While the latter works easily within a tolerance of +/-1 to 2%, this value ranges from +/-2% to 1% in belt weighers. The other disadvantageous aspect consists in the cost for belt weighers and particularly in the operating expense for maintenance, cleaning, servicing, etc. Belt weighers are expensive and can only be successful in the processing of very highly priced products such as chemical substances. Not many belt weighers are found in foodstuff and feedstuff plants for the aforementioned reasons, but also because belt weighers require relatively large horizontal dimensions. In past years, great efforts have also been made to monitor the product flow with entirely different measuring systems, but without greater success.
Another special problem consists in the throughput capacity, which regularly amounts to well over one ton per hour in present-day milling operations; the usual amounts are 10 . . . 20 . . . 50 or more tons per hour for the respective production flows to be measured.